This invention relates to slave controlled forward, reverse or third point measurements of group delay and/or attenuation distortions of any of a number of transmission sections connected in a measuring loop between a local transmitter and a local receiver.
The principle of measuring group delay and attenuation distortions according to H. Nyquist and S. Brand in "Measurement of Phase Distortion"; Bell System Tech. Journal 9; (1930), page 522 and modifications thereof are summarized in the copending U.S. patent application entitled "Method and Apparatus for Measuring the Group Delay Characteristics of a Transmission Path" that was filed for the same assignee and on the same day as this application. The contents of that application are included by reference.
There are certain transmission line configurations where it may be desirable to make a measurement at a remote point of a transmission section under test and to have the result available at a point in the network other than at that point where it was made.
For example, a commonly encountered measuring problem involves the measurement of group delay and attenuation distortions over a transmission section under test extending between the transmitter of a receiver-transmitter set and the receiver of another receiver-transmitter set, where both measuring sets are at remote locations from a local measuring station including a receiver-transmitter set, and the transmission path under test passes through the local measuring station. A closed loop has to be established from the local transmitter to the receiver of the measuring set at the remote end of the departing section, from the receiver to the transmitter at the same location, from this transmitter to the receiver at the other end of the transmission section with its two partial sections ending at the local measuring station, from this receiver to the transmitter at the same location and back to the local receiver via the arriving section.
In the German Patent specification No. 2,221,256 an apparatus is disclosed for selective remote control and remodulation mode which contains manually operable switches interconnected between the receiver and transmitter of each remote measuring set. A remote operator has to establish or interrupt certain circuit connections in order to establish remote control or remodulation mode operation. Furthermore, if measurements over extended sections are performed and consequently the level of the reference carrier signal suffers substantial attenuation losses, these losses have to be compensated by the remote operator in the remodulation mode, if an unallowable dynamic range of the measuring apparatus or of the transmission path should be avoided.